Shale Barren Rock-cress

Arabis serotina

Description

Shale barren rock-cress, Arabis serotina, rock-cress is an erect, flowering biennial that grows to a height of 1-2 ft (30-60 cm). Young, first-year plants grow close to the ground as inconspicuous basal rosettes. Mature, second-year plants have a spreading, compound inflorescence of many tiny (0.2 in; 2-3 mm) whitish flowers.

The species can easily be confused with A. laevigata var. burkii, which also grows on shale barrens. Although there are subtle morphological differences between the two, they can most readily be distinguished by their flowering periods. While all varieties of A. laevigata bloom in April and May, A. serotina blooms from late June through September.

Habitat

Shale barren rock-cress is the rarest of several plant species found only in dry, exposed, mid-Appalachian habitats known as shale barrens. These unique shale slopes are found in the lower Appalachian Mountains from Pennsylvania south to Virginia and West Virginia, and are characterized by steep southern exposures, sparse vegetative cover, and a hot, dry summer microclimate. Shale barrens support 18 endemic plant species, several of which are candidates for listing under the Endangered Species Act: mountain pimpernel (Taenidia montana ), Kate's mountain clover (Trifolium virginicum ), and Allium oxyphilum.

Distribution

Shale barren rock-cress has been found only in western Virginia and eastern West Virginia, on south-to southwest-facing shale barrens at elevations between 1,300-2,500 ft (395-760 m). This highly restricted range is believed to reflect the natural distribution of the species rather than the outcome of recent land-use changes or the lack of suitable habitat elsewhere.

In 1987 about 130 mature plants were recorded at 13 sites in five Virginia counties (Allegheny, Augusta, Bath, Highland, and Rockbridge). A 1985 survey of West Virginia shale barrens located 13 populations with a total of 700 individuals. By the time the species recovery plan was published in 1991, there were 34 extant populations of shale barren rock-cress located in six Virginia and three West Virginia counties. Discovery of new populations has increased the known numbers of plants. The West Virginia populations occur in Greenbrier, Hardy, and Pendleton counties; four new West Virginia populations were discovered in the summer of 1995. Virginia populations occur in Allegheny, Augusta, Bath, Highland, Page, Rockbridge and (possibly) Shenandoah counties, although the Shenandoah population was last seen in 1957 and may have been extirpated.

Nineteen of the known populations occur in the Monongahela (West Virginia) and George Washington (Virginia) National Forests; of these, by 1991, 13 had been proposed for further administrative protection. One Virginia population is owned and protected by the Commonwealth, and the protection needs of a West Virginia population on U. S. Navy land have been studied under a cooperative agreement. By 1991, no protection had been initiated for the populations on private land.

Threats

Browsing by deer and habitat destruction caused by road construction are the main threats to the shale barrens rock-cress. White-tailed deer browse heavily on the plant. Eight of 11 West Virginia populations surveyed in 1985 showed a 30% loss of seed to deer browsing. Deer populations are increasing in these two states and browsing will continue to present a threat to the species.

Road construction has been a major factor in destruction of shale barren habitat. Five shale barrens in West Virginia that supported known rock-cress populations and three in Virginia have been partially destroyed by road construction.

Although 34 populations of the plant were known as of 1991, most had under 100 plants and many have fewer than 10 individuals, making the species vulnerable to local extirpation. Small populations are particularly vulnerable to catastrophic loss by a stochastic event causing reproductive failure, such as a tree falling or seed dispersal into an unsuitable habitat.

The populations in National Forests are relatively secure from human disturbance but remain vulnerable to damage by deer. At least one West Virginia population is on a shale barren leased by the Nature Conservancy, which is attempting to secure voluntary protection for additional populations.

Conservation and Recovery

The 1991 Recovery Plan for the shale barren rock-cress notes it may be possible to initiate delisting by 2002, if individual recovery tasks proceed on schedule. Before the species can be delisted, the species must be reclassified to threatened; to qualify for reclassification, a number of recovery criteria must be met; among them, the confirmation of the existence of 20 demonstrably self-maintaining populations distributed throughout the species' range; and permanent protection of the habitat for these populations. Seeds must also be stored to prevent extinction in case of catastrophic loss of natural populations. Delisting will be initiated when, in addition to the reclassification criteria being met, 15 additional self-maintaining populations and their habitat are permanently protected.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035-9589
Telephone: (413) 253-8200
Fax: (413) 253-8308
http://northeast.fws.gov/

References

Bartgis, R. 1989. "Distribution and Status of Arabis serotina (Brassicaceae) in West Virginia." Proceedings of the West Virginia Academy of Sciences.

Keener, C. 1983. "Distribution and Biohistory of the Endemic Flora of the Mid-Appalachian Shale Barrens." Botanical Review 49:65-115.

U. S. Fish and Wildlife Service. 1991. "Shale Barren Rock Cress Recovery Plan." U. S. Fish and Wildlife Service, Newton Corner, Massachusetts.

Wieboldt, T. 1987. "The Shale Barren Endemic, Arabis serotina (Brassicaceae)." Sida 12(2): 381-389.